In the course of processing a photographic element containing an imagewise exposed silver halide emulsion layer reduced silver can be formed either as a direct or inverse function of exposure. At the same time, at least a low level of reduced silver formation also occurs independently of imagewise exposure. The term "fog" is herein employed to indicate the density of the processed photographic element attributable to the latter, usually measured in minimum density areas. In color photography fog is typically observed as image dye density rather than directly as silver density.
Over the years a variety of differing materials have been introduced into silver halide emulsions to inhibit the formation of fog. Research Disclosure, Vol. 176, December 1978, Item 17643, Section VI, lists the more commonly employed fog inhibiting agents. Research Disclosure is published by Kenneth Mason Publications, Ltd., The Old Harbourmaster's, 8 North St., Emsworth, Hampshire P010 7DD, England.
It is known to employ as fog inhibiting agents compounds having two aromatic nuclei linked by two divalent sulfur atoms and analogous compounds in which one or both of the sulfur atoms are replaced by selenium atoms. Exemplary of such fog inhibiting agents are those disclosed by Millikan et al U.S. Pat. No. 3,397,986, Pollet et al U.K. Specification No. 1,282,303, and Herz et al U.S. Pat. No. 3,811,896 and French Pat. No. 2,135,176. While the two Herz et al patents are counterparts, the French patent contains pertinent subject matter which is not common to both.
Lelenthal et al U.S. Pat. Nos. 4,144,062 and 4,152,155 disclose photothermographic imaging systems employing an oxidizing agent and a reducing agent in combination with a catalyst, which in one form can be silver halide. The oxidizing agent is an organotellurium (II) or (IV) compound which in one form can be comprised of two aromatic nuclei linked by two divalent tellurium atoms. Compared to the catalyst, the oxidizing agent is present in relatively high concentrations.
Asahi Japanese Kokai No. 57817/78, laid open May 25, 1978, discloses the use of a variety of tellurium compounds as chemical sensitizers for silver halide emulsions. In one of a variety of differing forms the tellurium compounds can satisfy the formula EQU R.sub.1 --Te--Te--R.sub.2
wherein R.sub.1 and R.sub.2 are organic groups, such as substituted or unsubstituted alkyl or aryl groups or carbonyl containing organic groups. Aryl substituents disclosed are methyl, ethyl, methoxy, amino, dimethylamino, hydroxyl, and halogen.